Primary purpose of this study is to evaluate PTFE grafts as a substitute for saphenous vein in bypass grafting for coronary artery disease. With the aid of cardiopulmonary bypass procedures several groups of dogs will be generated: 1) Saphenous vein graft bypasses to LAD. 2) Impra (a PTFE) grafts to LAD. 3) Possibly - gore-tex grafts to LAD. Subsequently all animals will undergo cardiac catheterization at regular intervals of 2-3 months, 8 months and 1 year postoperatively. A small number of animals from each arm of the study will be sacrificed following catheterization at each interval for gross and microscopic evaluation of the grafts.